1. Field of the Invention
The present invention relates to a magnetic disk apparatus which is a memory apparatus or, in particular, to a magnetic disk apparatus comprising a performance specification identification circuit capable of identifying the individual performance specification of the magnetic disk apparatus with a simple configuration.
2. Description of the Related Art
In recent years, the performance of a magnetic disk apparatus has come to depend to a large measure on the characteristics of the heads or the magnetic disks providing a storage medium. For this reason, it is necessary to strictly manage the characteristics of the heads and the disks, and the magnetic disks must be used under conditions conforming to the respective characteristics.
The characteristics of the heads and magnetic disks have conventionally been managed mainly on the assembly line for the disk apparatus. Specifically, a worker makes it a practice to visually check the number of the magnetic disks and the number of the heads or the type of the control IC of the magnetic disk apparatus in the process of assembly, and attaches a label or the like conforming to the configuration of the magnetic disk apparatus on the reverse side of the housing to thereby identify the type of the magnetic disk apparatus.
The latest trend, however, is toward an increased number of types of heads and magnetic disks, of the magnetic disk apparatus, which are supplied from a plurality of suppliers. Further, in order to increase the range of articles by changing the storage capacity of the magnetic disk apparatuses, different numbers of heads or magnetic disks are sometimes mounted in the same housing. The characteristics of the heads and the magnetic disks may thus vary from one supplier to another. In the case where the heads and the magnetic disks are purchased from different suppliers, therefore, the characteristics corresponding to the respective parts are preferably recognized by the control circuit of each magnetic disk apparatus to control the apparatus with a control constant most suitable to each part.
With the increased number of combinations of the number and type of the heads and the magnetic disks and the number of the types of the control IC for the control circuit delivered from different suppliers, it has become increasingly difficult to set up or manage individual magnetic disk apparatuses conforming to the respective component elements thereof.
Another current trend is toward an increased use of a composite head including a MR (magnetoresistive) head and an inductive head for the magnetic disk apparatus. The resultant problem is a change in the characteristics of the magnetic disk at low temperatures (deterioration of the overwrite (O/W) characteristic) that adversely affects the data read-write characteristics, and a solution to this problem is desired.
In a magnetic disk apparatus, the signal reproduced by the head is passed out of the housing through a flexible circuit board mounted on the side of the carriage, and led to a printed circuit board arranged on the reverse side of the housing. The head IC and the servo IC for demodulating the read signal supplied by the head are often mounted on the flexible circuit board (hereinafter referred to as the flexible cable).
In the magnetic disk apparatus, the number of the magnetic disks accommodated in the same housing are sometimes changed by a modification to the specification by the supplier of the magnetic disk apparatus. In the case where the head IC for processing the signals from the head or circuit components such as the capacitors and resistors forming the peripheral circuit are mounted on the flexible cable, a separate circuit for identifying the specification information of the magnetic disk apparatus is mounted on each of the flexible cable and the printed circuit board.
The identification circuit for the specification information of the magnetic disk apparatus generally includes a pull-down circuit having a resistor mounted on the flexible cable and a MCU (microcomputer unit) as a control IC for the magnetic disk apparatus mounted on the printed circuit board 79.
This specification information identification circuit for the magnetic disk apparatus can represent two states according to the presence or absence of the resistor in the pull-down circuit. In the case where a magnetic disk apparatus having the same housing specification has two specifications for the magnetic disk, one involving a single magnetic disk, and the other involving two magnetic disks, for example, the two states are distinguished by changing the resistance value of the resistor.
In this method, however, only two states can be represented by each pull-down circuit. If the type and the number of the heads is to be identified in addition to the number of magnetic disks, therefore, an increased number of the pull-down circuits are required, thereby posing the problem of an increased number of connectors, MCU pins and resistors leading to an increased overall cost.
Further, for the specification information to be obtained on the number of each type of magnetic disks and the type and the number of the heads of each magnetic disk in the process of fabrication of a magnetic disk apparatus, such information must be read from the label attached to the individual magnetic disk apparatuses. In the conventional method, the bar code printed on the label is read by a tester, so that a program code and read/write parameters suited to each housing of the magnetic disk apparatus are downloaded.
With regard to the deterioration of the overwrite characteristic at low temperatures which has recently posed a problem, on the other hand, it is known that the read/write characteristic can be improved by increasing the write current. An excessively increased write current, however, is liable to destroy the data in adjacent tracks by write expansion.
A means for solving these problems is disclosed in JP-A-64-79904, JP-A-1-137409 and JP-A-1-166361, in which a resistor is mounted on both the flexible cable in the magnetic disk apparatus and on the printed circuit board (hereinafter referred to simply as the printed board) outside the magnetic disk apparatus. The two resistors are connected in series, so that a reference voltage is applied to them and the partial voltage appearing at the junction point is identified by a voltage comparator.
The method described in the above-mentioned patent publications, however, requires a series-connected resistor and a comparator for detecting a partial voltage at the junction point thereof for each identification item of the magnetic disk apparatus. For identifying a multiplicity of items, therefore, a correspondingly increased number of voltage comparators are required, giving rise to a new problem of an increased size and hence an increased cost.
Another problem of the method described in the above-mentioned patent publications is that the internal temperature of the housing of the magnetic disk apparatus cannot be detected and therefore the deterioration in the overwrite characteristic at low temperatures cannot be prevented.